Results have shown that it is possible to reduce both the concentration and pretreatment time of the polyvalent metals and still obtain higher stable levels of fluoride in enamel than that obtained after APF treatment alone. These new pretreatment conditions caused considerably less dissolution of the enamel surface than previously used pretreatment times and salt concentrations. Scanning electron microscope studies have shown massive surface coatings after metal ion pretreatment followed by APF application. Microprobe analysis suggests that the coating contains metal ions and fluoride without substantial penetration of the metal into the enamel. The effect of these optimal conditions on artificial lesion formation awaits histological evaluation.